1. Field of the Invention
The invention relates to calibration tools and methods for calibrating an apparatus that is used to test for the presence of trace amounts of substances of interest.
2. Description of the Related Art
Terrorism risks continue to increase at transportation facilities, government buildings, banks, restaurants, hotels and other locations where there is a significant flow of pedestrian or vehicular traffic. As a result, virtually all airports and many other buildings now include apparatus for detecting trace amounts of explosives.
Narcotics are illegal and insidious. Furthermore, it is known that many terrorists organizations fund their terrorism through the lucrative sale of narcotics. Accordingly, many airports and other public buildings recognize the need to check for narcotics.
U.S. Pat. No. 5,491,337 discloses a device that employs and ion trap mobility spectrometer to test for trace amounts of contraband. The ion trap mobility spectrometer can be operated in a negative mode to test for trace amounts of explosives. The ion trap mobility spectrometer disclosed in U.S. Pat. No. 5,491,337 also can be operated in a positive mode to check for trace amounts of narcotics. Additionally, the apparatus of U.S. Pat. No. 5,491,337 can be switched quickly from the positive mode to the negative mode so that a single sample can be tested for the presence of trace amounts of either explosives or narcotics. Detectors that incorporate the technology disclosed in U.S. Pat. No. 5,491,337 are marketed by GE Security, Inc. and perform very well. The disclosure of U.S. Pat. No. 5,491,337 is incorporated herein by reference.
Prior art detectors have used many techniques for delivering a sample into the detector to test the sample for substances of interest. For example, some detectors employ small flexible fabric-like traps that can be wiped across a package or piece of luggage. The trap removes residue from the surface of the package or luggage. The trap then is placed in an apparatus, such as an ion trap mobility spectrometer, that tests the residue on the trap for trace amounts of explosive materials or narcotics.
Detectors that rely upon wiping a flexible fabric trap across a piece of luggage impede the flow of pedestrians through a check point, and hence typically are used only for spot checks. Additionally, an explosive or narcotic detector of this type would not identify a contraband worn by a passenger or other pedestrian who was not carrying luggage.
U.S. Pat. No. 6,073,499 discloses a walk-through detector. The detector shown in U.S. Pat. No. 6,073,499 operates under the principle that a boundary layer of air adjacent to a person is heated by the person. This heated air adjacent a person is less dense than air further from the person. Less dense air rises. Accordingly, a thermal plume of air flows up adjacent to a person. Minute particles, including particles of explosives or narcotics, will be entrained in this thermal plume of air and will flow upwardly from a person. The walk-through detector disclosed in U.S. Pat. No. 6,073,499 employs an ion mobility spectrometer or ion trap mobility spectrometer to detect microscopic particles of interest that are likely to be entrained in the thermal plume of air flowing upwardly adjacent to a person who walks through and pauses briefly in the detector. The walk-through detector disclosed in U.S. Pat. No. 6,073,499 is very effective for detecting whether a person is carrying explosives or narcotics and whether the person has recently handled explosives or narcotics. The disclosure of U.S. Pat. No. 6,073,499 is incorporated herein by reference.
The walk through detector of U.S. Pat. No. 6,073,499 is extremely effective and operates very quickly. However, the device is large and is not suitable for many access points.
Pending U.S. Patent Publication No. 2005/0019220 discloses a small detector with a slot through which a card may be swiped. This device operates under the theory that trace amounts of particles of interest will be transferred from the hand of a passenger or other pedestrian to the card. These trace amounts of particles of interest then are removed as the card is swiped through the slot and particles removed from the card can be analyzed to determine whether substances of interest are present. U.S. patent application Ser. No. 10/929,915 discloses another small detector apparatus that can be used quickly to detect for the presence of substances of interest. More particularly, the detector of U.S. patent application Ser. No. 10/929,915 includes a thin metal disc or a thin metal drum that rotates into proximity to a window. A passenger or other pedestrian who desires access places his or her fingers on the metal disc or drum. Residue from the fingers are transferred to the metal. The removal of the fingers from the metal disc or drum generates a signal that causes the area that had been contacted to move into the detector. The metal material is heated sufficiently to vaporize residue thereon and the vaporized residue is transported into the ion trap mobility spectrometer. The disclosures of U.S. Patent Publication No. 2005/0019220 and U.S. patent application Ser. No. 10/929,915 are incorporated herein by reference.
The above-described detectors work extremely well. However, variations in atmospheric pressure, humidity and temperature can affect the performance of these known detectors. For example, a detector used in Denver may function differently than a detector used in Florida. Furthermore, detectors used at any geographic location may perform differently from day-to-day as climactic conditions change. Therefore, it is necessary to calibrate the detectors periodically to ensure that the detectors function with sufficient accuracy to detect trace amounts of explosives or narcotics based on a very small sample size for the ambient conditions that exist on a particular day and at a particular location. Manufacturers of these detectors, such as GE Security, Inc., generally recommend calibration on a daily basis, such as at the start of every work day. Devices that wipe a fabric trap across an item of luggage are calibrated by using a calibration trap that is known to have small amounts of the substance of interest thereon or a substance that is known to have a very similar signature. This calibration trap could be stored in a sealed container that is kept near the detector apparatus for access by the security personnel. Calibration traps, however, are not particularly useful for the more recent detector devices that analyze residue on the fingers of a person who desires access.
In view of the above, it is an object of the subject invention to provide an inexpensive tool that can be used for calibrating a contraband detector so that the detector can accurately test for substances of interest.